1. Field of the Invention
The present invention relates to a valve timing control apparatus for an internal combustion engine which varies a valve timing (an opening-and-closing timing) of an intake valve and/or an exhaust valve of an engine due to a rotational phase of a camshaft with respect to a crankshaft of an internal combustion engine being varied.
2. Description of the Related Art
As a valve timing control apparatus for an internal combustion engine, there is an apparatus disclosed in Japanese unexamined patent publication No. 2000-303865. In this type of conventional valve timing control apparatus for an internal combustion engine, a crank angle sensor outputting a crank angle signal at a reference rotational position of a crankshaft and a cam sensor outputting a cam signal at a reference rotational position of a camshaft are provided thereto, and a rotational phase of the camshaft with respect to the crankshaft is detected on the basis of a deviation angle between the reference rotational positions.
In the above-described conventional structure, a rotational phase is detected for each constant crank angle (rotational period of the camshaft). However, feedback control (valve timing control) based on such a detected result of a rotational phase is generally executed in each micro-unit time.
Therefore, at the time of low-speed rotating, a detection period of rotational phases is made longer than an execution period of valve timing control, and the rotational phases cannot be detected with sufficient frequency in terms of the controllability. In such a case, there is a problem that a deviation with a target rotational phase is calculated on the basis of a rotational phase different from an actual rotational phase, and a feedback manipulated variable is calculated on the basis of an incorrect deviation, and the controllability deteriorates.
Here, rotational phase detecting means which can detect a rotational phase in an arbitrary timing regardless of the rotational period of the camshaft is provided, and by carrying out detection of a rotational phase in accordance with a request such as a valve timing control period or the like, it is possible to detect a rotational phase with sufficient frequency in terms of the controllability at the time of low-speed rotating as well.
However, in a case in which a rotational phase can be detected in an arbitrary timing, usually, as compared with the above-described conventional structure, there is a high possibility that the output characteristics or the like of the rotational phase detecting means (detecting element) are varied over time, and a new problem that the precision in detecting rotational phase, i.e., the precision of a valve timing control deteriorates due to a variable (deviation) in the output characteristics is brought about.